1. Field of the Invention
The present invention relates to a bushing, more particularly, to a bushing and a group of bushing for mounting a suspension cross-member on a vehicle, to a suspension cross-member fitted with such bushing, and to a vehicle on which such a suspension cross-member is mounted.
2. Description of the Related Art
Conventionally, bushing is used to mount a suspension cross-member to the bottom of a vehicle body. The structure of such bushing is disclosed in Japanese Patent Publication No. 2001-71944 for example, which comprises an outer member, an inner member which is inserted into the outer member and through which a stud on the body projects downwardly, and a elastic member disposed between the outer member and the inner member. In the structure, the bushing has an axial length sufficient for penetrating the cross-member and is press-fitted into respective mounting holes from one direction. To mount the cross-member to the body, the cross-member is fitted with the bushing, positioned in place with respect to the body so that the body studs are inserted into the inner member, and then secured to the body via nuts fitted onto the studs. The previous adjustment of a spring constant of the elastic member of the bushing achieves intended ride comfort and handling stability of the vehicle.
In a meantime, the application of a preload to the elastic member is well known for satisfying the needs of the ride comfort and the handling stability. For example, in the bushing structure constituted as described above, the elastic member has an extended axial length so as to protrude in the axial direction or in the vertical direction by a predetermined amount, and the nut is screwed until the elastic member is compressed between the body or the cross-member and the nut. Thus, after the cross-member is mounted on the body, the elastic member is provided with the predetermined amount of preload. In accordance with the structure as above, the elastic member is interposed between the body and the cross-member so as to be compressed in the vertical direction, so that the frequency dependence is reduced to improve the ride comfort, and the intended spring constant is produced in the elastic member. That is, the proper axial preload of the elastic member beneficially provides the vehicle with the increased ride comfort and handling stability at once.
The cross-member is supported on the body via a plurality of bushing, each of which is press-fitted into the cross-member and secured to the body. Accordingly, the variation in the amount of preload among the respective mounting portions or bushing may cause the degradation in the handling stability and ride comfort. To avoid the degradation, the accurate amount of preload should be applied to each bushing in the axial direction, thus measures are required for adjusting the screwing amount of each nut and for ensuring that the elastic member adequately deforms at the abutting portion on the body and the cross-member. Even with the measures described above, however, the variation in dimensional accuracy inevitably occurs in the cross-member or the bushing, which adversely affects the accuracy of the amount of the preload. Though the problem can be eliminated by precise management of the dimensional accuracy of parts, it causes the parts cost to rise and the production efficiency to decrease.
In addition, as disclosed in Japanese Patent Publication 2000-145854 for example, the bushing is typically fitted to bushing-attaching holes in suspension parts by press-fit operation. In the press-fit operation, a jig is used, which displaces the bushing in the fitting direction while abutting on the bushing. However, the jig may deform the bushing in the presence of friction between the bushing and the bushing-attaching hole, which also results in the variation in the amount of preload.
In view of the problem above, an object of the present invention is to achieve the excellent handling stability and ride comfort of the vehicle at once, by the provision of a bushing for mounting the cross-member to the bottom of the body which decreases the amount of the variation in preload for easily and reliably attaining the intended amount of preload with the reduced cost.
In accordance with the first aspect of the present invention, there is provided a bushing which is press-fitted into a top aperture and a bottom aperture of a bushing-attaching hole penetrating a suspension cross-member and fixed to a vehicular body by a stud and a nut for mounting the suspension cross-member to the bottom of the vehicular body. The bushing includes an outer member having an outer main body with a substantially cylindrical shape with an axial length shorter than one half of the axial length of the bushing-attaching hole of the suspension cross-member and an outer flange extending in the radially outward direction from an axial end of the outer main body, an inner member including an inner main body having a substantially cylindrical shape with an axial length longer than one half of the axial length of the bushing-attaching hole of the suspension cross-member and with an external diameter smaller than the internal diameter of the outer main body, an inner flange extending in the radially outward direction from an axial end of the inner main body with an external diameter larger than the internal diameter of the outer main body, and a through hole through which the stud can be inserted. The inner member is coaxially inserted into the outer member so that the inner flange and the outer flange are on the same side with respect to the axial direction and an elastic member is disposed between the inner member and the outer member and adhered to the inner main body, the inner flange, the outer main body, and the outer flange. When the bushing is press-fitted into the top aperture and the bottom aperture of the bushing-attaching hole until the outer flanges contact with the suspension cross-member before the bushing are fixed by the stud and the nut, the elastic members are substantially free from elastic deformation and provide a predetermined clearance between the other axial ends of the inner members. Moreover, when the bushing is fixed to the body by the stud and the nut, the elastic members are elastically deformed by tightening the nut fitted onto the stud so that the inner members are axially displaced with respect to the outer members to abut on each other.
Accordingly, for mounting the cross-member with a fastening mechanism, the bushing is press-fitted into the top aperture and the bottom aperture of the bushing-attaching hole, and the fastening mechanism is tightened until the ends of the inner members of the bushing abut on each other. Therefore, the operation as above easily provides an intended axial preload corresponding to the predetermined clearance in the bushing in a reliable manner with little or no variation in the amount of the preload among the bushing in respective bushing-attaching holes, after the cross-member is fixed to the body.
Preferably, the outer member further includes a jig-abutting portion provided in the outer flange, on which a jig can abut for press-fitting the bushing into a bushing-attaching hole in the suspension cross-member, and a reinforcing portion formed as a bending portion of the outer flange for preventing deformation of the outer member when the bushing is press-fitted with the jig.
Accordingly, in the press-fit operation, the reinforcing portion prevents deformation of the outer member due to the friction between the bushing and the bushing-attaching hole, which ensures the accurate amount of preload provided in the bushing.
Further it is preferred that the jig-abutting portion be a planar surface which continues to and is at substantially a right angle with the outer main body in a cross section including the central axis of the bushing.
Accordingly, in the press-fit operation, the jig can press the portion close to the outer main body of the outer flange, so that the deformation of the outer flange is avoided in combination with the effect of the reinforcing portion.
Still further it is preferable that the reinforcing portion include a slanted surface which is at an angle larger than the right angle with the outer main body, and the inner flange may include a tilt which faces the slanted surface substantially in parallel.
Accordingly, the elastic member is compressed by two surfaces facing in parallel with each other, so that the accuracy in preload provided in the bushing increases. Moreover, such an advantage is available by use of a part of the reinforcing portion.
In accordance with a second aspect of the present invention, there is provided a plurality of bushing.
In accordance with a third aspect of the present invention, there is provided a suspension cross-member fitted with bushing or a plurality of bushing.
In accordance with a forth aspect of the present invention, there is provided a vehicle on which a suspension cross-member is mounted.
These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description of preferred embodiments and accompanying drawings.